Ahead of Stage 4 of the 2026 Tour de France Femmes last month, riders encountered an addition to the familiar pre-time-trial ritual of bike measurements and equipment checks: officials were paying particular attention to their chests.
Several Women’s WorldTour teams had reportedly complained that riders appeared to have greater chest volume in time trials than in road stages. The suspicion was that some competitors were using padding, ice or other material underneath their skinsuits to effectively create a “chest fairing” for an aerodynamic advantage.
The UCI regulations, specifically Article 1.3.032, state that clothing and accessories may not modify a rider’s morphology and prohibit non-essential elements added to, placed beneath or integrated into clothing. The UCI’s technical guidance for Article 1.3.032 also prohibits products or substances applied to the body or clothing to improve aerodynamics.
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However, neither document establishes how much padding a sports bra may contain. They also do not provide a specific protocol for examining one, and the sudden bra checks drew a lot of critique as well as questions around the exam’s invasiveness, bra structure, breast shape and size, and, of course, whether a padded bra can actually make a rider faster.
While initial chest fairing studies found drag reductions of up to 3.6 percent, new CFD modelling from AiRO suggests that sports-bra-sized marginal gains may be negligible. At least in AiRO’s test, a push-up bra is more likely to lift expectations than speed.
What the studies say
(Image credit: Andy Jones)
Much of the understanding of chest fairings comes from a 2024 peer-reviewed paper by Bert Blocken, Fabio Malizia and Thijs van Druenen in the Journal of Wind Engineering and Industrial Aerodynamics.
The researchers used computational fluid dynamics, or CFD, to examine seven chest fairing configurations on a male cyclist in a time trial position. The simulations were then validated through wind-tunnel testing. Their best-performing configuration reduced drag by 3.6 percent, which is a potentially significant advantage in a race decided by fractions of a second.
However, not every fairing was beneficial. Some configurations increased drag, and the researchers concluded that a rider would need dedicated wind-tunnel tests or CFD simulations to determine whether a particular shape would provide an advantage. The study found that a chest fairing can be effective, though it did not conclude that additional chest volume is inherently faster.
The size of the fairing matters greatly. The study’s largest drag reduction came from a substantial, purpose-built form modelled on the chest fairings used by some triathletes, far from the shape or padding amount of a conventional sports bra.
AiRO, a company that provides CFD-based aerodynamic modelling to bike fitters, has now tested a narrower question: whether comparatively small changes in chest volume can produce the same effect. That is, changes small enough to be hidden inside a bra.
What AiRO tested
AiRO CFD modelling testing various chest volumes using a female rider model wearing a Specialized Evade helmet.
(Image credit: AiRO)
AiRO created a digital female rider in a fixed cycling position and modelled three chest volumes: small, medium and large. The company tested each version with two helmets, the Specialized Evade and the Ekoi Pureaero, because aerodynamicist Ingmar Jungnickel argues that changes around the chest could affect airflow reaching the rider’s head and equipment farther downstream.
Jungnickel told Cycling Weekly that the virtual athlete was based on a rider measuring 175cm (5’9″) and weighing 60kg (132lbs).
With the Ekoi helmet, AiRO reported drag differences of −0.1%, +0.2% and +0.3% percent across the three chest configurations. Plus means more drag; minus means diminished drag. Jungnickel described the differences as “nothing at all,” writing that “not one configuration produced a measurable gain.”
With the Specialized Evade, all three chest configurations were approximately 2.2% slower than its reference, while changing from the smallest to the largest volume barely altered the result.
“Small chest volume changes, as they could be hidden in a sports bra, do not seem to make riders faster,” Jungnickel concluded.
AiRO also modelled what it called a “proper fairing,” akin to a water bottle stuffed down a jersey as has been seen by some male riders in the past. This model featured a rider with the Giro Aerohead and the Specialized Evade.
The drag reductions were −0.7% on the Giro Aerohead, −0.1% on the Specialized Evade.
“The best case is a possible small advantage that is within measurement uncertainty. That is with an object under the suit, on a male rider, in a full time trial position,” AiRO concluded.
“Changing chest volume by the amount a padded sports bra can change it did nothing on either helmet, for either sign, at any of three sizes,” AiRO concluded.
AiRO acknowledged the limitations to its findings. For one, the company tested only one rider model per sex, and Jungnickel said the effect could vary with “bust volume, torso length, shoulder width and how closed the rider’s position already is.”
“A single athlete tells you the mechanism exists and roughly how big it is for that rider, but it doesn’t give a universal number,” he said.
AiRO also used a parametric human model fitted to images rather than a 3D body scan. Jungnickel said that approach allowed the company to preserve the same underlying geometry between tests, avoiding variations caused by scanning artefacts.
That consistency may improve comparisons within AiRO’s test, but the analysis remains a company-authored demonstration rather than a peer-reviewed study. AiRO has not published the full solver settings, mesh-independence analysis or numerical uncertainty calculations that would allow outside researchers to evaluate its results in detail.
Even with those limitations, Jungnickel said the central finding was clear: “Bra stuffing is at least not clearly a benefit.”
So what to believe?
(Image credit: Getty Images)
Jungnickel argues that AiRO’s results do not necessarily contradict Blocken and his co-authors. The disagreement, in his view, lies in the interpretation of the data.
According to AiRO’s reading of the Blocken paper, the three smallest fairings changed drag by +0.54, +0.39 and −0.68 percent. Under that convention, two made the rider marginally slower and one produced a small improvement. The widely reported 3.6-percent reduction came from a much larger, solid fairing measuring 313mm wide and 87mm tall.
Jungnickel argued that sub-one-percent effects may fall within the practical uncertainty of CFD, wind-tunnel or velodrome testing and may vary from rider to rider.
“At differences that small, most serious fit changes offer a larger benefit,” he said.
The two analyses therefore point to a more nuanced conclusion: a large, carefully shaped fairing can reduce drag, but small changes in chest volume do not appear to provide a consistent or readily measurable advantage.
So, before you start stuffing socks into your sports bra, the evidence calls for restraint. A large, carefully shaped fairing can reduce drag, but modelling suggests that bra-sized changes offer no reliable shortcut to speed. It appears that for most cyclists, a better position and fit remain safer – and legal – places to find free watts.
